Stroboscopic device.



G. JENSEN.

STROBOSCOPIC DEVICE.

APPLICATION nuzp OCT. 9. ms.

1,251,669, Patented Jan. 1, 1918.

WITNESSES: M ly INV ENTOR W e 51/ 71 nan/015a I A ORNEY UNITED STATESPATENT OFFICE.

GUNNAR JENSEN, OF SWISSVALE, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSEELECTRIC AND MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

STROBOSCOPIC DEVIGE.

Specification of Letters Patent.

Application filed October 9, 1915. Serial No. 54,949.

To all whom it may concern: 7

Be it known that I, GUNNAR JENSEN, a citizen of the United States, and aresident of Swissvale, in the county of Allegheny and State ofPennsylvania, have invented anew and useful Improvement in StroboscopicDevices, of which the followingis a specification.

My invention relates to stroboscopic devices and particularly to.devices that are used to determine the percentage slip ofalternating-current dynamo-electric machines.

The object of my invention is to provide a device, of the aboveindicated character, that is simple in construction and accurate over awide range of application.

The single figure of the accompanylng drawings is a perspective view ofa strobescopic device embodying my invention.

A dynamo-electric machine l'is connectedto an alternating-currentcircuit 2, and a stroboscopic device 3 1s electrlcally connected to thecircuit 2 and mechanicallyv connected to the rotor 4 of thedynamoelectric machine 1 for the purpose of determining the percentagesllp thereof.

The stroboscopic device 3 comprises a sup- 7 porting standard 5,avibrating device 6 and a gear box 7. The vibrating device 6 comprises amagnetizable core member 8, a winding 9 and a resilient armature 10. Thearmature 10 is supported by a block 11, and its effective length is sovaried that its period of vibration is normal with respect to thefrequency of the alternating current that traverses the winding 9. Theblock 11 surrounds the standard 5 and is provided with a thumb screw 12for the purpose of securing it in position. The magnetizable core member8, a resistor 13 and an electric lamp 14 are also supported by the block11. The lamp 1 1 is provided with a refiector 15 for the purpose ofilluminating- 18 and 19 that are spaced apart by spacing Patented J an.1, 1918.

members 20. Journaled in the plates 18 and 19 are three shafts orspindles 21, 22 and 23. A gear wheel 24 is mounted upon the shaft 21, asis also a disk 25. The disk 25 is provided with oppositely disposedrad1al slots 29 the number of which is an integral factor of the numberof poles in the machine-1. The gear wheel 24 is provided withtwenty-five teeth and is adapted toen- -gage two gear wheels 26 and 27that aremounted on the shafts 22 and 23, respectively. The gearwheels'26 and 27 are provided with twenty-three and twenty-four teeth,respectively. However, the gear wheels may have various numbersof teeth,accordlng to the ratios desired. A universal couphng 28 is adapted toconnect the rotor 4 of the machine 1 to any one of the shafts 21, 22 and23.

If the coupling 28 is 'connected to the.

shaft 21 the disk 25 will be rotated at the same speed as the rotor ofthe machine 1, and, if the rotor of the machine 1 .rotates atsynchronous speed the armature 10 will appear in the same position eachtime, when viewed through the openings 29 in the disk 25, or, 'in otherwords, the armature 10 will apparently stand still. However, if therotor 4 is rotated at a speed slightly different from that ofsynchronism, the armature 10 will be found in a slightly differentposition ateach observation and will apparently oscillate from side toside, similar to a pendulum. Since the armature oscillates insynchronism with the circuit 2, the apparent oscillations of the samewill correspond to the slip in alternations, and the slip will be equalto the apparent oscillations per minute divided by the frequency of thecircuit in alternations per minute.

It is evident that the greater theslip the greater will be the number ofapparent oscillations of the armature, and, if the slip is very high,these will become so rapid as to be impossible to determine accurately.It has been found, by numerous trials, that about 150 oscillations perminute is the maximum that can be ordinarily observed with accuracy.However, if the machine l is a sixty-cycle machine, 150 oscillations perminute will correspond to 2.08 per cent. slip. Since a large proportionof sixty-cycle machines have a percentage slip varying from two to eightor more, I provide the gear box 7 by means of which the disk 25 may berotated at a speed that is a predetermined definite amount lower thanthe speed of the. rotor 4, thus permitting higher s'lip values to beaccurately determined. When the rotor 4 is connected to the shaft-23 thedisk 25 will rotate four per cent. slower than the rotor 4, and, thus,if the armature 10 appears to stand in one position when observedthrough the openings 29, the'slip of the rotor 4 will be four per cent.If the rotor 4 is connected to the shaft 22 the disk 25 will be rotatedat a speed that is eight per cent. lower than the speed of the rotor 4,and, if the armature 10 appears to stand still when observed through theopenings 2, the .slip of the rotor 4 will be eight per -cent. Thus, withthe gear ratios, as sh own,

four per cent. and eight per cent. may be taken as reference points, andthe slip above and below these particular values may be determined andadded or subtracted from either 4 or 8 to obtain the true percentageslip. Assuming that the rotor 4 is connected to the shaft 23, thepercentage slip equals 4 plus or minus, the observed oscillations pervminute divided b the frequency of the circuit 2 in alternations perminute. Whether the sign is plus or minus may be readily determined byvarying the load upon the machine 1 and noting whether the oscillations.

increase or decrease with an increase in load. If the oscillationsdecrease, 1t 1s evident that the percent. slip isunder 4 or that thesign is minus.

The disk 25 may be provided with any number of openings 29, according tothe number of poles in the machine 1, and the ratio of the gear wheels24, 26 and 28 may be varied according to the range of slip to bedetermined.

The vibrating portion 6 and the gear box 7 are adapted to be moved alongthe supporting standard 5 for the purpose of facilitating observationand for facilitating the connections of the device to the'rotor of themachine to be tested.

My invention is not limited to the particu lar construction illustrated,as many modifications may be madetherein without departing from thespirit and scope of the invention as set forth in the appended claims.

I claim as my invention:

1. 'In a stroboscopic device for an alternating-current motor, thecombination with a supporting standard, a vibratory member, and meansadjustable along the standard for for actuating the same in synchronismwith the alternating current, of a rotatable disk adjustably mounted onthe standard, and a universal connection between the rotatable disk andthe motor.

3. In a stroboscopic device for a dynamo- 'electric machine, thecombination with a supporting standard, and a vibratory memberadjustable to various positions along the standard, of a rotatable diskhaving openings therein, means for operatively connecting the rotatabledisk to the machine, and means for adjusting the position of the diskwith respect to the vibratory member.

4. In a stroboscopic device for an altermating-current motor, thecombination with a supportingstandard and a vibrating membar that isvibrated at the frequency ot the alternating current, of a rotatabledisk having slits therein, a gearing operatively connected to the diskand the rotatable member of the motor for driving the disk either insynchronism with the rotatable member or in a predetermined speedrelation therewith, and means for adjustably securing the vibratingmember, rotatable disk and the gearing to the supporting standard.

5. In a stroboscopic device for an alternating-current motor, thecombination with a supportin standard, a vibratory member adapted to evibrated in synchronism with the alternating current, and means forsecuring the vibratory member to various positions along the standard,of a rotatable disk, and a gear mechanism operatively connected betweenthe disk and the movable member of. the motor and supported by thestandard.

6. In a stroboscopicdevice for an alternating-current motor, thecombination with a supporting standard, a vibratory member adapted to bevibrated in synchronism with the alternating current, and means forattaching the vibratory member to the supporting tandard, of a rotatabledisk, a gear mechanism operatively connected between the disk and themovable member of the motor, and means for adjusting the position of thedisk with respect to the supporting standard.

7. In a stroboscopic device for an alternating-current motor, thecombination with a supporting standard, a vibratory member adapted to bevibrated in synchronism with the alternating current, and mean forattaching the vibratory member to the supporting standard, of a gearbox, a disk ro- 5 tatably mounted on the gear box, a gear mechanismwithin the gear box, means for connecting the gear mechanism to therotatable member of the motor and means for shifting the position of thegear box along the supporting standard.

In testimony whereof, I have hereunto subscribed my name this 28th dayof Sept,

GUNNAR JENSEN.

